1. Field of the Invention
The present invention relates to a spindle rotation driving device such as a spindle motor for rotating a plurality of information recording mediums stacked such as a hard disk, optical disk, optical card, and the like, an information recording/reproduction apparatus, and an information recording medium manufacturing method.
2. Related Background Art
An information recording/reproduction apparatus used in the manufacture, inspection, and the like of information recording mediums such as a hard disk, optical disk, optical card, and the like mounts a spindle rotation driving device such as a spindle motor or the like for rotating a plurality of disks which are stacked.
FIG. 6 shows a conventional spindle rotation driving device. A spindle portion 110 which stands upright on the surface of a base 101 of the information recording/reproduction apparatus holds a stack of a plurality of disks D, and is rotated by a motor M0 disposed below the base 101.
The spindle portion 110 has a shaft 112 which is rotatably supported by a pneumatic bearing 111 fixed to the base 101. On the stationary side of the pneumatic bearing 111, a ring-shaped air pad 111a made up of a porous material and a pipe 111b for guiding clean air thereto are provided.
The plurality of disks D are stacked to sandwich a spacer S between neighboring disks D, and are clamped between a clamp 112a integrated with the shaft 112, and a hub 113 fastened to the upper end of the shaft 112.
The shaft 112 extends below the base 101 via a flange 112b disposed under the pneumatic bearing 111. A scale disk 115 of an encoder is mounted on the lower end of the shaft 112 and opposes an optical head 116.
A rotor 117 made up of a magnet integrated with the shaft 112, and a stator 119 consisting of a yoke 119a and coil 119b held by a motor housing 118 construct a motor which rotates the shaft 112. Note that the encoder is used in detection, control, and the like of the rotational speed of the motor.
Each spacer S is inserted to maintain parallelness of the disks D, and to suppress surface run-out upon rotation.
Upon fitting the disks D on the shaft 112, the central holes of the disks D are pressed against the shaft 112 alternately in opposing directions, so that the gaps formed between the shaft 112 and the central holes of the disks D are evenly distributed on the two sides of a rotation axis (spindle axis) O. In this way, dynamic unbalance caused by eccentricity of the disks D is suppressed.
Recently, an information recording apparatus is required to record large-size information, and therefore the recording densities and rotational speeds of recording mediums such as disks and the like are increasing. For this reason, smaller track pitches and strict management of track pitch errors are required. In order to meet such requirements, it is important to suppress not only synchronous and asynchronous vibrations but also eccentricity of each recording medium with respect to the spindle axis.
Compared to the required track pitch precision, the central hole of a disk as a recording medium has a very large hole diameter tolerance as standards, and eccentricity of a disk caused by this tolerance makes improvement in the track pitch precision difficult.
Any dynamic unbalance of the center of gravity upon rotating a disk causes whirling vibration, and vibrates not only the spindle axis but also a magnetic recording converter such as a magnetic head or the like via the base that fixes the motor at high rotational speed, thereby disturbing accurate alignment.
Furthermore, a stack of a large number of disks makes eccentricity correction of the disks harder, and enhances any already existing dynamic unbalance.
In the prior art, the surface run-out of each disk in the horizontal direction is suppressed using the spacer, but no mechanism for correcting any dynamic unbalance caused by eccentricity of each disk is added. For this reason, the disks are alternately pressed against the shaft to uniformly distribute gaps between the inner circumferential surfaces of the disks and the shaft, thus suppressing the dynamic unbalance. However, such measure maximizes the gap between each disk and the shaft, and the eccentricity amount of each disk becomes xc2xd the tolerance of the diameter of the central hole of the disk.
Upon building a system within a limited space, it is difficult for a single fluid bearing that rotatably supports the lower portion of the shaft to suppress vibrations of the distal end portion of the disk stack, as indicated by the broken line in FIG. 6.
The present invention has been made in consideration of the problems that remain unsolved of the prior art, and has as its object to provide a spindle rotation driving device which suffers less whirling vibrations due to a dynamic unbalance upon rotating a stack of recording mediums such as disks and the like, an information recording/reproduction apparatus, and an information recording medium manufacturing method.
In order to achieve the above object, a spindle rotation driving apparatus of the present invention comprises a spindle portion having a shaft for holding a stack of recording mediums, a first fluid bearing for rotatably supporting the spindle portion, a motor for rotating the spindle portion, an aligning member which is pressed against an upper end portion of the shaft in an axial direction, and a second fluid bearing for maintaining the aligning member in a non-contact manner with respect to the upper end portion of the shaft.
Preferably, the aligning member is coupled to a floating plate which is free to float or be chucked on a lift stage by a fluid pressure.
Preferably, an air pad for injecting fluid is provided on a cylindrical surface of the shaft, and eccentricity of the recording mediums fitted on the shaft is prevented by a fluid film formed by the fluid.
Preferably, air of the second fluid bearing is supplied from the first fluid bearing via an inner pipe of the shaft.
Preferably, air of the air pad of the shaft is supplied from the first fluid bearing via an inner pipe of the shaft.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.